


Written in Bone

by TrashTheater



Category: Undertale (Video Game)
Genre: Fontcest, M/M, Soulmate AU, The levels of obliviousness in this fic are too dang high!
Language: English
Status: Completed
Published: 2018-11-10
Updated: 2018-11-10
Packaged: 2019-08-21 19:16:51
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,938
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16582466
Author URL: https://archiveofourown.org/users/TrashTheater/pseuds/TrashTheater
Summary: Papyrus hated his Soulmate Mark. His soulmate seemed like some kind of creep. Sans agreed.





	Written in Bone

**Author's Note:**

> Based on the soulmate AU where the first thing your soulmate will say to you appears somewhere on your body. God I love me some soulmate AUs!

“Sans.”

Sans opened his eyes blearily. Around him New Home Hospital bustled with moderately busy nurses and meandering patients who were too restless to stay in bed. He rubbed at his sockets sleepily, wondering when he’d fallen asleep. He really didn’t want to miss the big moment. 

“Sans,” came his fathers voice again and he jumped, startled. Gaster stood in a nearby doorway, exhausted but with an undeniable look of pride and overwhelming joy. “Are you ready?” 

Sans scrambled down from the hospital chair and raced past his fathers legs into the light pink hospital room. The light in there was softer then in the hallway. He barely had a moment to look around before he was swept up by his father and placed firmly in another chair, this one a lot more comfortable then the last. His feet swung nearly a foot off the floor but he didn’t mind. He was still growing. He’d be as tall as his father in no time. 

“Stay right here a moment…” Gaster told him, before crossing the room to fetch something small from the clear bassinet beside the hospital bed. It was wrapped up tight in a white blanket. Sans squirmed with barely concealed excitement as Gaster took far too long to return. “Be very careful… support his head… just like that…”

The small, warm bundle was placed gently in his lap, and Gaster maneuvered his arms until they were all in the proper position. 

“Sans,” He introduced softly. “This is your new baby brother.”

Nestled deep in the blanket bundle was the tiniest, little white skull he’d ever seen before in his life. Itsy bitsy little sockets peered up at him with open curiosity and he couldn’t help but marvel at how teeny-tiny the little monster was. Were all babies that small once? Was he that small once? How could anything be that small? 

There was a soft sound from the bed and after a quick, half-phrased warning Gaster returned to his wife's side, leaving the boys alone. 

Sans smiled down at the little baby bones. The little monster responded immediately, sockets scrunching up to accommodate the look of pure unabashed happiness on his face. His little arms were quick to wiggle loose of the blanket and stretched up, reaching for him with the teenie-est weenie-est little fingers he could even imagine. 

He felt his soul melt into a gelatinous mess. Careful not to disrupt his hold, he availed one of his hands and held it out. The tiny, _tiny_ little bones wrapped around the tip of his pointer finger and he was _gone_. 

“hey baby…” He choked out, overwhelmed with love and warmth. His little baby brother. He would protect that sweet smile forever. He would never let anything bad happen to him, ever. 

The little arm attached to that tiny hand began to glow faintly. Sans leaned a little closer before realizing what it was. The little skeleton was getting his Soul Mark. Normally, monsters developed them in the first few years of their life, but it wasn’t unheard of for them to develop particularly early. 

Still, an unexpected dead settled in his non-existent stomach as he carefully pulled the arm closer, squinting to try and read the miniscule writing on the winy white bone. It was faint, but he could make it out, clear as day:

_hey baby_

“oh no…” he whispered under his breath. The baby wiggled his arm once, before letting out a sound, somewhere between a shriek and a giggle. Sans sockets widened at the alarmingly familiar sound. He rubbed his arm against his leg until he managed to push his sleeve up. 

His own Soul Mark wasn’t a sentence, but a shamble of half-finished letters. Looking at it now, it looked suspiciously like the sound his brother had just made. 

“no, no, no, no, no…” He looked back and forth between the marks. That wasn’t supposed to happen. He was pretty sure siblings weren’t supposed to be soulmates. Did he do something wrong? Did he mess it up somehow?

He noticed Gaster moving near the bed and shoved down the sleeve, tucking the blanket up and over the baby bones little arms wrapping him back up. After a moment, their father returned and carried them both over to the bed. 

Their mother smiled as they were deposited in her lap, before Gaster sat on the bed beside them. “Sans,” she begain sweetly. “This is Papyrus. Say ‘hi’.”

“hi papyrus!” He blurted out quickly, hoping they hadn’t heard him before. He wasn’t sure what would happen if they knew, but he didn’t want them to know. He didn’t want them to know the first thing he’d done as a big brother was mess up his brothers soulmate. 

His parents smiled. Papyrus squirmed. Sans tried not to cry. 

. . .

Papyrus _hated_ his Soul Mark. Absolutely loathed it. And he had ever since he’d been old enough to understand exactly what the thick, clear lettering marking up his radius was: Some monsters rude, and frankly uncreative, catcall! 

It had been rather disappointing to realize that his first interaction with his soulmate was going to start as some sort of lame pick up attempt. He supposed it was a little idilic to hope for a more romantic meeting. After all, it was already ‘written in bone’ as Sans would say. Still, it was certainly not the type of meeting he’d have preferred. 

Worse yet-! That little line sentenced him to a life of responding to any old stranger that shouted at him on the street or any drunk monster sliding up to him at a bar. He didn’t even like bars!

Of course the Great and Exceptionally Clever Papyrus had concocted a fool-proof plan to weed out any false prospects. Any time someone decided to call him ‘Baby’ he would respond with a very clear, very unique phrase sure to help his soulmate recognize him immediately! “I AM THE LEGENDARY SPAGHETTI MASTER!” Sans helped him come up with it. He thought it was very clever. It was the perfect way to let his soulmate know who he was. 

Fortunately, he hadn’t gotten the opportunity to use it. Monsters were notoriously good at small talk and the few monsters he’d even suspected of flirting had all started with a much more respectable greeting. It only further cemented his fears about the type of person his soulmate was. 

As such, he did not get excited when he would meet someone new when picking Sans up from Grillbys, nor when a stranger started a conversation with ‘hey-‘. He never considered taking the River Persons boat to New Home to casually search the bars there to potentially fast track the destined meeting. And he certainly never laid awake in bed running his fingers over the letters, thinking maybe it was just a little flattering someone wanted to call him ‘Baby’… 

He would never do any of that! He was perfectly content to wait as long as possible to meet his creep of a soulmate! 

To be perfectly honest, he was just happy he still had the chance to recognize his soulmate. Poor Sans said he had some barely legible baby babble, meaning he’d already met his soulmate back when they were both babies. There wasn’t any way to know for sure who his soulmate was now. Babble Soul Marks weren’t too terribly uncommon so they were pretty hard to pair up unless a teach or a parent manages to catch it when they happen. 

Worse yet-! Sans was such a lazybones, he wasn’t even looking! Every time Papyrus brought it up, Sans just brushed it off with a resigned acceptance. He said searching would just leave him ‘bone tired’ anyways. But Papyrus knew better. It definitely bothered him. Sans always kept it covered, even from Papyrus and he didn’t even like to talk about it. 

Luckily for him, he had the bestest brother in the whole Underground and Papyrus was not going to let him give up that easily! Maybe Papyrus had to wait to meet his soulmate, but that didn’t mean Sans did!

It had taken no time at all to create a forum on Undernet for all monsters with Babble Marks to try and find their soulmates. Sans hadn’t been interested in joining, but that was fine. papyrus was happy to put the work in, if it would make Sans happy. He tracked down all the monsters Sans could have met in infancy and arranged some meetings. Sans was reluctant, but agreed after some plea-like encouragement. 

Papyrus was pretty sure he’s nailed it on the very first date. After the third, he realized it was going to be a little more difficult then he’d hoped. However, he would not give up! Even if Sans said he probably should. He was going to find his brothers soulmate! 

He just wish he knew where to look…

. . . 

Papyrus glanced at the clock for the third time in the last minute and sighed. Sans was taking forever! He finally rested his chin on his folded arms and sagged on the kitchen table, staring at his empty plate. He really should clean up but he found himself just pushing it away. 

Sans was late. Well, not really. They had never established any actual return time, but he’d always returned home from those ‘dates’ well before Papyrus had finished eating, so that was just the time span he’d come to expect. 

That was a good thing though, wasn’t it? That meant the date was going well. Maybe Papyrus had finally found the right one? That should have made him excited, but instead he just looked at the clock again and groaned. 

It was getting late-late. Like ‘Papyrus would have picked him up from Grillby’s by now and be getting ready for bed’-late. He opened his phone. No calls. No messages. 

He probably shouldn’t wait up, he thought with a blush. If it was actually his soulmate, Sans might not come home until the morning. He tried not to think about it. But, Sans would send him a message if he was going to stay out all night, wouldn’t he? 

Papyrus gave it another half an hour before he hit send on the **> > HOW’S IT GOING? << **he’d typed an hour before. He didn’t want to rush them just because he wanted his brother to hurry home. It occurred to him, if he did find Sans soulmate, he would be out late all the time… 

His phone buzzed a second later. 

**> > good. didnt c the time. omw now <<**

He was coming home!? That was exactly what Papyrus had wanted to avoid! He quickly typed out to stay and enjoy himself, but didn’t manage to hit ‘send’ before the door opened. 

“UGH! SANS!!!”

“hey bro,” He replied, strolling in with a wide grin at Papyrus’s greeting. “sorry i’m late.” He made a beeline for the fridge. 

“DON’T APOLOGIZE! WHY DID YOU COME HOME!?” 

“what do you mean? of course i’m gonna come home,” He started shuffling through the fridge. 

“I MEAN- YOU SAID YOU WERE HAVING FUN!”

He grabbed a plate of spaghetti and closed the door. “oh yeah. had a great time. we had a lot in common. she even likes my puns. we were talking so much we actually missed the reservation.” He laughed and put the plate in the microwave. 

Papyrus held his breath, waiting for his brother to continue, but Sans was too focused on the food. “… … …-AAAAAAND?!” 

“what?”

Papyrus sighed exasperated. “AND: IS SHE YOUR SOULMATE? DID YOU FEEL LIKE, ANY KIND OF CONNECTION?!”

“oh yeah… nah.”

“WHAT DO YOU MEAN ‘NAH’!?” 

“didn’t feel nothing,” He answered, grabbing the now hot plate and sitting down across from him. “made a new friend though. thanks!” 

Papyrus pouted as Sans dug into the food with the gusto only Sans had when facing his world class pasta. Well, that was a little disappointing. It did really seem like she’d been the one. Theoretically, Sans should be able to feel _something_ , but it wasn’t an exact science. Papyrus crossed his arms. Maybe they should try again? 

Then again… maybe he was rushing things… After all, there was no rush. Sans would find his soulmate when the time came, right? Just like Papyrus would. Until then, maybe it would be best to just let things remain the way they were. 

His phone ‘ding’ed with an alert. 

**> > Sans is heading home. Had a great time! Tnx for setting it up! <3 <<**

Papyrus clicked out a reply.

**> > GOOD TO HEAR IT! DID YOU FEEL ANYTHING? <<**

The response came almost immediately. 

**> > Oh sure. Happy to go again anytime! <<**

He sat up straighter. 

**> > YOU FELT SOMETHING!? SOULMATE SOMETHING!? <<**

**> > XD No, but I’d love to go out again. I think Sans already knows who his SM is anyways. LOL <<**

Papyrus looked up startled. “You… you told her you already know who your soulmate is?”

Sans froze mid-bite. “uh…” His eyes darted nervously for a second. “don’t… see how i could have done that… given the circumstances- are you talking to her?”

Papyrus frowned and clicked out a reply. 

**> > WHY DO YOU THINK THAT? <<**

“paps, give me the phone.” Sans reached towards it, but Papyrus leaned back, holding it out of range. 

“WHY?”

Sans began to sweat, then started rooting around in his pockets for his own phone. 

**> > Just seemed like it. <<**

**> > He talks like he knows him. <<**

**> > Got all sad and wistful when I brought it up. <<**

**> > And he always says ‘he’ LOL. <<**

**> > I mean: I’m just guessing! <<**

**> > In fact I’m 100% wrong! <<**

**> > You have the wrong number! <<**

_*The monster you are trying to reach has tossed their phone into the core. Please try again later.*_

Papyrus looked down at Sans who was starting at him nervously over the top of his phone. 

“SANS…-!”

“well-p! guess i’m done! food was great paps!”

“ARE YOU KIDDING ME!? YOU KNOW WHO YOUR SOULMATE IS!? WHY DIDN’T YOU TELL ME!?”

Sans held up his hand placatingly. “look, i don’t know what she said, but-“

“IT SOUNDS LIKE YOU KNOW _HIM_ PRETTY WELL.”

He stopped, wincing. “ok… well. i can see where she would get that idea, but-“

“WHY DID YOU LET ME SET YOU UP WITH SOMEONE WHO ISN’T YOUR SOULMATE!?” 

“i-i mean- you were so excited about that. and i told you not to bother. but i really don’t-“

“WHO IS IT?”

Sans hesitated and Papyrus watched him run quickly over his options. “uh… i… no clue.”

The kitchen was quiet for a moment aside from the soft ticking of the clock. Papyrus let the words sink in, feeling his soul squeeze in response. “YOU…” He began with a pained wince. “YOU DON’T TRUST ME…” 

Sans made a similar expression. “pap, no, it’s not that…”

“IT IS! YOU KNOW WHO IT IS; YOU’VE ALWAYS KNOWN WHO IT IS!” She was right. In hindsight, it explained a lot of the suspicious things Sans had said and done before, like how confident he was about the dates not working out. And she was double right! Papyrus had heard him say ‘he’ before! Multiple times! “A-ANDFOR WHATEVER REASON, YOU DON’T TRUST ME ENOUGH TO TELL ME.”

Sans sighed, wearily rubbing at his sockets. “pap, i…” Papyrus looked at him and he wilted. “…alright… yeah. i know who it is…”

It hurt a little more to hear him admit it. Sans had been lying to him for so long… but he felt a little better hearing the truth. Sans knew who his soulmate was. He felt a twinge of excitement along with a strong case of nerves. 

“WHO IS IT?”

Sans sighed again. 

Papyrus waited, longer then he wanted before realizing with a sinking feeling Sans probably had a good reason to hide it from him. 

“DID…” Papyrus began fearfully, almost not wanting to hear the answer. “DID SOMETHING HAPPEN TO HIM?”

Sans looked up. “oh! no, no! it’s not anything like that!”

Papyrus let out a sigh of relief. But that still begged the question… 

“he’s… fine. he’s perfect actually,” Sans chuckled, his voice resonating with that overwhelmingly fond tone Papyrus had only ever heard him use when talking about him. It was sweet, and he most certainly did not feel a sharp stab of jealously in his soul. “but… we would’t… he deserves someone better then me anyway…”

Papyrus jumped out of his chair. “WHAT ARE YOU TALKING ABOUT, BROTHER! HE’S YOUR SOULMATE! YOU TWO WERE DESTINED FOR EACH OTHER! HE’S LOOKING FOR YOU TOO! ANYONE WOULD BE HAPPY TO BE YOUR SOULMATE!”

Sans smiled warmly, before shaking his head. “thanks pap. but i’m not going to tell him. and i’m not telling you. it’s not that i don’t trust you, it just um, i do think you will try to _do_ something about it.”

Papyrus started to argue because he wanted to know- he needed to know who his brothers soulmate was, but Sans was right. He would try to fix whatever Sans thought was wrong. He frowned. He _really_ needed to know-! 

“I S-SUPPOSE YOU ARE CORRECT, BROTHER,” He struggled to force out the reluctant words. “I MAY HAVE A HABIT OF DOING EXACTLY THAT. I MEAN, I VERY MUCH THINK THAT YOU ARE COMPLETELY MISINFORMED ABOUT WHETHER OR NOT YOUR SOULMATE DESERVES YOU, BUT I AM PERHAPS NOT THE MOST SECRETIVE OF MONSTERS.”

Sans chuckled, that fond sound again. “i know.”

Papyrus rubbed his arm, thinking about his own soulmate. “HOW DID YOU MEET? I THOUGHT YOUR MARK WAS BABBLE.”

He shrugged. “it is… he’s a bit younger then me, so i met him when he was still a baby. i read his mark and it was the stupid thing i’d just said and… i don’t know. for a long time, i thought i’d messed something up… like i forced the mark there somehow… sometimes i still think i did…”

“SANS, THAT’S NOT THE WAY THAT WORKS.”

“yeah, I know,” He shook his head. “look it’s late. i’m not gonna tell you anymore. but at least you can stop looking to set me up on dates, okay?”

That was hardly the most importnat factor to come out of that conversation, but Papyrus let it slide. It was late, even if he was far too buzzed to sleep now. He helped Sans clean up from dinner and he even still got a bedtime story, although it didn’t help be settle down any. He just kept watching Sans, like maybe he would say or do something to give away the answer. Sans just read the story like normal and wished him ‘goodnight’ before going to bed. 

Unable to sleep, Papyrus rolled up his sleeve and looked at the mark on his arm. 

_hey baby_

He rubbed his fingers over the letters with a sigh. Why didn’t Sans want to be with his soulmate? Sure, Papyrus wasn’t sure he liked the implication of his own Soul Mark, but he knew that didn’t really matter. It was his soulmate. He knew he would love them completely, cheesy pickup lines and all. 

_hey baby_

Was it someone Sans still knew? Someone he was still close with? Would it be harder to live close to your soulmate and not be with them, or farther away and never see them?

_hey baby_

It was someone younger then him, so they wouldn’t remember meeting.

_hey baby_

Someone Sans wouldn’t want to know they were soulmates. 

_hey baby_

Someone Sans would have met when they were a baby. 

_hey baby_

Papyrus stared at the mark on his arm, sockets widening. 

Oh. 

OH! 

How had he never noticed!? He kicked off the blankets and flew out of his room. Sans’s door was unlocked (luckily, as he would not have hesitated to kick it down. He had plenty of practice replacing them.) and he burst in without knocking. 

“SANS!”

Sans was still awake, having been scrolling through his phone in bed. His sockets were wide with shock. 

“geez, pap! you scared the bejesus-“

“WHAT WAS THE FIRST THING YOU SAID TO ME AFTER I WAS BORN?”

The room became very quiet as Sans turned into a stone statue.Papyrus glared. Sans wasn’t going to get out of it that time. 

Finally, expression not faltering, his eye light darted slight to the left. “said ‘hi papyrus’.”

“REALLY?” Papyrus questioned. “ ‘HI PAPYRUS’? DID YOU SAY ‘HI PAPYRUS’? OR DID YOU SAY ‘HEY’ BECAUSE YOU ALWAYS SAY ‘HEY’, AND DID YOU SAY ‘BABY’ BECAUSE YOU DIDN’T KNOW MY NAME YET, AND WOULD ANY OF THIS EXPLAIN WHY MY SOUL MARK IS WRITTEN _IN COMIC SANS, SANS_!?” 

Sans noticeably flinched. “…i… isn’t that a weird coincidence I was hoping you’d never notice because it’s… just a coincidence…?”

“REALLY?” He stepped forward and Sans scrambled out from under the covers, standing in the far corner. “THEN LET ME SEE YOUR ARM. BECAUSE I’M WILLING TO BET WHAT FONT YOURS IS WRITTEN IN.”

“i’m not really liking my odds on that one, so i don’t think i’ll take-“ Papyrus lunged at him, landing on the bed as Sans took a shortcut across the room. “h-hold on a second! lets not jump to conclusions, papyrus!”

Papyrus didn’t stop, vaulting off the bed and missing Sans by an inch. “I CAN’T BELIEVE YOU ARE MAKING PUNS AT A TIME LIKE THIS!”

“in my defense-“ Sans admitted. “that one was an accident.”

“IF YOU WEREN’T MY BROTHER, SOMEONE I REALLY CARE ABOUT, AND APPARENTLY MY SOULMATE-! I COULD ACTUALLY STRANGLE YOU RIGHT NOW!” Sans dodged his next move but Papyrus had picked up on a pattern and got a head start. 

He tackled Sans and they rolled across the dirty carpet. Sans struggled to escape even as Papyrus pinned him down and yanked up the sleeve covering his arm. 

There it was. A mass of half-formed letters, that looked more like a sound then any given word… in a very distinct papyrus font.

Sans stopped struggling after another second, and then sagged into the carpet. “pap, i… i didn’t want you to find out… i know if’s not really what you were hoping for and-“

*CLACK*

Sans flushed as Papyrus quickly cut him off by pressing their teeth together. The skeleton kiss lasted only a second, before Papyrus pulled back and stole another one.

“NYEH HEH HEH!” He giggled softly, feeling excitement course through his soul. Sans was his soulmate. His soulmate and no one else’s! “HEH HEH- SANS, YOU BONEHEAD! YOU SHOULD HAVE TOLD ME! I’VE BEEN LOOKING FOR YOU AND YOU COULDN’T HAVE BEEN MORE IN FRONT OF MY FACE!” 

Sans still looked in disbelief, his whole skull turning that cute blue tint. “b-but i-i thought you hated your soul mark- and i-“

“THAT WAS,” Papyrus flushed a little too, also looking away. “BEFORE I KNEW IT WAS SOMETHING SWEET. THIS IS WAY BETTER THEN IT BEING SOMETHING CREEPY.”

“it’s still sorta creep-“

Papyrus cut him off with another kiss. And another. And another, until Sans started to relax, his eye light getting softer.

“pap…”

“IT’S SWEET,” He repeated. “AND WHILE I MAY OR MAY NOT HAVE LIKED THAT PARTICULAR ENDEARMENT IN THE PAST, I DO RATHER THINK THAT IT’S PERFECTLY FINE, AS LONG AS IT’S COMING FROM YOU.” 

Sans looked surprised, before finally giving him a real smile. “what’s that? would you like me to call you ‘baby,’ baby?” 

Papyrus felt the blush from the top of his skull all the way down his spine. “Y-YES! THAT WOULD BE VERY ACCEPTABLE!”

“baby…” Sans grinned wider, holding up his arm. “guess you gotta call me this, then.”

“SANS!” 

He laughed. Papyrus kissed him. They both laughed. It was very, very sweet. 

**Author's Note:**

> That was some soft and buttery cheese for you! Just a little one shot I haaaaad to write down. I think it came out pretty good! But let me know what you think!


End file.
